1. Field of the Invention
This invention relates generally to ion sources, and, more specifically, to an improved ion source including a back-streaming electron dump.
2. Description of the Related Art
Radio Frequency (RF) driven ion sources have achieved a prominent role in semiconductor manufacturing, for both material deposition and etch, as well as for ion implantation. These ion sources have additionally been used as neutron generators for a variety of applications ranging from material identification for homeland security operations, to sources for linear accelerators widely used in medical applications.
These ion sources have generally been provided as chambers, to which the gas to be ionized is introduced, and then RF energy applied to the gas to form a plasma. Typically the RF energy is coupled to the gas using an RF antenna. Different antenna configurations have been used to drive the ion source, such as an internal antenna, an external helical antenna, and an external planar antenna. Lifetime has always been an issue for internal antennas. This has been largely overcome by the use of external antennas, particularly external planar antennas. However, for these external antennas, coupled to the plasma through a dielectric window, such as a quartz window, the inner surface of the quartz window is subject exposure to back-streaming electron bombardment, which results in localized, non uniform heating of the window, in turn inducing localized stresses, which over time can lead to cracking or breaking of the window.